1. Field of the Invention
This invention relates to an automatic bar-loader for lathes provided with linear sensors of the position of the bar-pusher. More generally this invention relates to an automatic lathe including such a loader.
2. State of the Prior Art
In the case of movable parallel drive-head lathes the lathe mandrel, in addition to starting bar rotation, moves the bar along its axis forward and backward several times during machining of a workpiece. In addition, upon unloading of a machined workpiece, the mandrel returns on the bar with collet open and then, with collet closed, advances the bar the desired amount.
In this manner, the tools only move transversely to the bar. The speed at which the mandrel moves can even be 40 meters per minute with accelerations near 1 g. The loader bar-pusher must obviously follow the mandrel during its sudden shiftings. This tracking must be very precise because otherwise the bar could slip out of the bar-pusher collet or be too compressed with catastrophic consequences for the machining.
In the prior art, synchronization of mandrel and bar-pusher generally takes place through a mechanical connection which however has a very complicated structure and involves considerable costs.
In the case of lathes with fixed parallel lathe drive head, the lathe mandrel starts rotation of the bar which is machined by tools placed on slides which move transversely and longitudinally to the workpiece. The bar is thus moved axially only by the bar-pusher during feeding into the mandrel of the new section to be machined. In other words, when a workpiece has been machined and detached from the bar, the mandrel collet opens and the loader must provide for advancing the bar by the amount desired for machining of the next workpiece. This advancement is generally not done in a very precise manner and the solution adopted in the prior art to remedy this is to position in front of the bar a retainer against which the bar is stopped. But this involves a considerable increase in total time to obtain a workpiece because the retainer must be positioned in front of the bar, often accompanying it in its advance, and then return to the rest position (3 to 8 seconds per workpiece can be lost). In addition, the retainer occupies a place that could be occupied by a machining tool. It is clear that in known loaders, devices and completely different outfitting are necessary to be able to feed a movable or fixed parallel lathe drive head.
The general purpose of this invention is to remedy the above mentioned shortcomings by making available a loader that can easily follow the shifting of the mandrel with greater precision when coupled to a movable parallel lathe drive head.
Another purpose of this invention is to make available a loader that can adapt easily and rapidly to use with a movable or fixed parallel lathe drive head without the need of mechanical bar-retainer devices typical of the prior art.